Insights into the carbon nanotube effect on the electrochemical performance of red phosphorus anode

Red phosphorus (Red P) is considered the most promising anode material for sodium-ion batteries (SIBs) because it possesses the highest theoretical capacity. However, its large volume expansion leads to rapid capacity decay, and its low conductivity limits fast charge–discharge capability, hindering the practical application. Here, Red P/single-walled carbon nanotube (SWCNT) and Red P/multi-walled carbon nanotube (MWCNT) composites were prepared by an evaporation–condensation method. After 100 cycles, Red P/SWCNT delivers a discharge capacity of 1512.6 mAh·g⁻¹, demonstrating stable long-term cycling performance, fast rate capability, and high initial Coulombic efficiency (ICE). The stress of Red P/SWCNT decreases from 7.2 (initial cycle) to 0.6 GPa (long cycle), whereas that of Red P/MWCNT decreases from 8.5 (initial cycle) to 1.7 GPa (long cycle) due to an approximately 30 nm thicker solid–electrolyte interphase (SEI) compared with SWCNT. The lower stress in Red P/SWCNT results in minimal cracking and a significant reduction in irreversible Na₃P formation, which is central to improving the electrochemical performance. These findings show that constructing a flexibl and highly conductive SWCNT network can effectively mitigates the stress caused by volume expansion and prevents the crack propagation in Red P. This work provides theoretical guidance for the development of Red P-based anodes for SIBs.